Hoists, operable between several positions such as haul or wind, hold or brake, and lock, and which operate from a single lever, are known in the art as shown, for example, by U.S. Pat. No. 3,773,294 issued Nov. 30, 1973. It is also known to utilize a shunting circuit across the armature of a motor associated with a hoist so as to provide, in effect, a dynamic brake to the gear drive system connected thereto, when the hoist is in a hold or lock position. Such shunting devices undesirably do, however, permit, especially when overloaded, some creep to occur within the gear drive train and accordingly permit some load movement. It would thus be desirable to provide a supplemental braking system to prevent such creep.
The present invention accomplishes these aims by the combination of a system utilizing dynamic hold braking by means of a shunted motor, and a subsequent locking of the gear train by an additional mechanical locking system in combination with the shunt control; both systems controllable sequentially by the same lever mechanism. This novel combination allows loads being hauled or hoisted to be temporarily maintained in a hold or dynamic brake position by the shunting system, and thereafter positively locked in hold position by a mechanical interlock with the gear train. As the bulk of the braking is designed to be accomplished by the motor shunt, the mechanical lock need only provide an incremental force, and thus need not be extremely rugged and hence costly construction.
The present invention thus effectively includes a hoist having a gear drive system in which an operating lever is selectively movable between a hold position in which the DC motor thereof is de-energized and in which a shunting switch is closed across the leads of the motor to form a dynamic braking action to the associated gear system, and a lock position in which the motor remains in the above disclosed shunted mode but wherein an added mechanical lock is engaged with the gear train, and a wind or haul position in which the motor is energized and both the shunt braking and locking systems are automatically disengaged.
Accordingly, the primary object of the present invention is to provide a power hoist which permits single lever operation between a hold position in which dynamic braking of the motor is accomplished by use of a shunt circuit, and a lock position wherein additional mechanical locking means is interengaged with the gear train thereof.
A further object of the present invention is the provision of a power hoist including the combination of dynamic braking by means of a shunt circuit across the motor and an additive mechanical gear train locking system wherein convenient and uncomplicated actuation of the mechanical system is provided through a novel bracket assembly.
Other objects, features, and advantages of the invention will become apparent when the description thereof proceeds when considered in connection to accompanying illustrative drawings.